diff --git a/docs/out-of-scope.md b/docs/out-of-scope.md
index 6314b132..12aeceee 100644
--- a/docs/out-of-scope.md
+++ b/docs/out-of-scope.md
@@ -17,3 +17,7 @@ But that doesn't mean it's not useful for other purposes. In the future, more co
 - *`frp`'s STCP or other setup that requires visitors' side configuration*
 
   If that kind of setup is possible, then there are a lot more tools available. You may want to consider secure tunnels like wireguard or zerotier. `rathole` primarily focuses on NAT traversal by forwarding, which doesn't require any setup for visitors. 
+
+- *Caching `local_ip`'s DNS records*
+
+  As responded in [issue #183](https://github.com/rapiz1/rathole/issues/183), `local_ip` cache is not feasible because we have no reliable way to detect ip change. Handle DNS TTL and so on should be done with a DNS server, not a client. Caching ip is generally dangerous for clients. If you care about the `local_ip` query you can set up a local DNS server and enable caching. Then the local lookup should be trivial.